I think it's less Seojin being undecided and more him caring too much about other ppl's opinion. He does like Cheol but it seems he's not so aware of his own feelings. Most of all, he's afraid of homophobia. I do think he needs to treat Cheol better (if not in a "chasing arc" way, at least for their relationship, be it romantic or platonic) but even if this is a very light story their relationship is not so black and white.

bro cheol deserves better than a freaking undecided person. - coming from someone who was liked but never pursued.
like why come to our completely peaceful life then left us literally hurting because they can't take the risk - I say FUCK YOU BITCHES.